1. Field of the Invention
The present invention is broadly concerned with new halogenated polymers which can be used as polymer binders in anti-reflective coatings, the resulting anti-reflective coatings, and methods of use thereof. More particularly, the inventive anti-reflective coatings comprise a polymer binder and a light attenuating compound wherein the polymer binder is halogenated, preferably on functional groups of the polymer binder. The coatings have high etch rates as well as good light-absorbing properties.
2. Description of the Prior Art
Integrated circuit manufacturers are consistently seeking to maximize substrate wafer sizes and minimize device feature dimensions in order to improve yield, reduce unit case, and increase on-chip computing power. Device feature sizes on silicon or other chips are now submicron in size with the advent of advanced deep ultraviolet (DUV) microlithographic processes.
However, a frequent problem encountered by photoresists during the manufacturing of semiconductor devices is that activating radiation is reflected back into the photoresist by the substrate on which it is supported. Such reflectivity tends to cause blurred patterns which degrade the resolution of the photoresist. Degradation of the image in the processed photoresist is particularly problematic when the substrate is non-planar and/or highly reflective. One approach to address this problem is the use of an anti-reflective coating (ARC) applied to the substrate beneath the photoresist layer.
Compositions which have high optical density at the typical exposure wavelengths have been used for some time to form these ARC layers. The ARC compositions typically consist of an organic polymer which provides coating properties and a dye for absorbing light. The dye is either blended into the composition or chemically bonded to the polymer. Thermosetting ARCs contain a cross-linking agent in addition to the polymer and dye. Cross-linking must be initiated, and this is typically accomplished by an acid catalyst present in the composition.
While these ARCs are effective at lessening the amount of light reflected back into the photoresist, most prior art ARC compositions are lacking in that they do not have a sufficiently high etch rate. As a result, prior art ARCs present significant limitations which make them difficult or impossible to use on submicron (e.g., 0.3 xcexcm) features. Accordingly, there is a need for faster etching ARCs which can be effectively utilized to form integrated circuits having submicron features.
The instant invention overcomes these problems by providing new halogenated compounds and polymers which can be used to form anti-reflective coatings (ARC) having substantially improved etch rates when compared to prior art ARCs. The instant invention also provides methods of using the inventive ARCs in the integrated circuit manufacturing process.
In more detail, the inventive ARCs comprise a polymer binder and a light attenuating compound (as used herein, the term xe2x80x9clight attenuating compoundxe2x80x9d is intended to include light absorbing compounds, chromophores, and any other compound which minimizes or prevents the transmittance of light) dissolved in a solvent system (either single or multiple solvents such as alcohols, ethers, glycol ethers, amides, esters, ketones, water, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, ethyl lactate, and p-chlorobenzotrifluoride). Preferred polymer binders include each of the following in halogenated forms: polyesters, polyacrylates, polyheterocyclics, polyetherketones, polyhydroxystyrene, polycarbonates, polyepichlorohydrin, polyvinyl alcohol, oligomeric resins (such as crown ethers, cyclodextrins, epoxy resins), and mixtures of the foregoing, with acrylic polymers being particularly preferred.
The polymer binder should be present in the ARC at a level of from about 30-90% by weight, preferably from about 35-85% by weight, and more preferably from about 45-85% by weight, based upon the total weight of the ARC taken as 100% by weight. The weight average molecular weight of the polymer binder should be from about 1,000-1,000,000 Daltons, and preferably from about 3,000-200,000 Daltons. The ARC""s preferably comprise from about 4-35% by weight, and preferably from about 8-32% by weight of a cross-linking agent, based upon the total weight of the ARC taken as 100% by weight. Preferred cross-linking agents include aminoplasts, epoxides, isocyanates, acrylics, and mixtures thereof. The inventive ARC""s preferably also include from about 0.1-5.0% by weight, and more preferably from about 0.3-4.5% by weight of a catalyst such as 2,2xe2x80x2-azobisisobutyronitrile. Finally, the solvent system is preferably present in the ARC composition at a level of from about 60-99% by weight, preferably from about 65-99% by weight, and more preferably from about 70-98% by weight, based upon the total weight of the ARC taken as 100% by weight.
The polymer binder comprises halogen atoms bonded thereto, preferably in sufficient quantities so that the polymer binder comprises at least about 5% by weight halogen atoms, preferably from about 20-80% by weight halogen atoms, and more preferably from about 30-70% by weight halogen atoms, based upon the total weight of the polymer binder taken as 100% by weight. Preferred halogen atoms are those selected from the group consisting of fluorine, chlorine, and bromine atoms.
It is particularly preferred that the halogen atoms be bonded to a functional group on the polymer binder rather than directly to the polymer backbone (i.e., rather than to an atom which is along the direction of polymerization). Of the total halogen atoms present in the polymer binder, it is preferred that at least about 5%, preferably at least about 10%, and more preferably from about 20-80% by weight of the halogen atoms be bonded to a functional group on the polymer binder, with the percentages by weight being based upon the total weight of all halogen atoms present in the polymer binder taken as 100% by weight. Even more preferably, each functional group has two and preferably three halogen atoms bonded thereto, preferably to the same carbon atom.
In one embodiment, the polymer binder comprises recurring monomers having the formula 
wherein: R in each monomer is individually selected from the group consisting of hydrogen and C1-C8 alkyls (preferably C1-C4 and more preferably C1-C2); X in each monomer is individually selected from the group consisting of the halogens and hydrogen halides, and preferably from the group consisting of xe2x80x94H2I, xe2x80x94HI2, xe2x80x94I3, xe2x80x94H2F, xe2x80x94HF2, xe2x80x94F3, xe2x80x94H2Cl, xe2x80x94HCl2, xe2x80x94Cl3, xe2x80x94H2Br, xe2x80x94HBr2, and xe2x80x94Br3; and m is from about 3-9,000, preferably from about 5-5,000, and more preferably from about 8-2,000.
Even more preferably, the polymer binder comprises recurring monomers having the formula 
wherein: R and Rxe2x80x2 in each monomer are individually selected from the group consisting of hydrogen and C1-C8 alkyls (preferably C1-C4 and more preferably C1-C2); X in each monomer is individually selected from the group consisting of the halogens and hydrogen halides, and preferably from the group consisting of xe2x80x94H2I, xe2x80x94HI2, xe2x80x94I3, xe2x80x94H2F, xe2x80x94HF2, xe2x80x94F3, xe2x80x94H2Cl, xe2x80x94HCl2, xe2x80x94Cl3, xe2x80x94H2Br, xe2x80x94HBr2, and xe2x80x94Br3; Xxe2x80x2 is selected from the group consisting of hydrogen and light attenuating compounds; m is from about 1-8,000, preferably from about 1-5,000, and more preferably from about 1-1,600; and n is from about 1-3,000, preferably from about 1-1,500, and more preferably from about 1-600. In this embodiment, the molar ratio of m:n can be adjusted as necessary to modify the etch rate and absorbance desired for the particular application. Preferably, the molar ratio of m:n is from about 1:9 to about 9:1, and more preferably from about 2:8 to about 8:2.
Regardless of the embodiment, the light attenuating compound can be bonded to the polymer binder or simply mixed therewith. The light attenuating compound should be present in the polymer binder at a level of from about 4-50% by weight, preferably from about 10-45% by weight, and more preferably from about 10-30% by weight, based upon the total weight of the polymer binder taken as 100% by weight. Preferred light attenuating compounds for use in the inventive ARCs include naphthoic acid, anthracene, naphthalene, benzene, chalcone, phthalimides, pamoic acid, acridine, azo compounds, dibenzofuran, and derivatives thereof.
Those skilled in the art will appreciate that various other compounds may be added to the inventive ARC as desired. For example, a cross-linking agent and a catalyst for the cross-linking agent can be added to the ARC.
The inventive ARCs are formed with the above-described compounds utilizing known ARC preparation procedures. For example, all of the components of the ARC (i.e., the polymer binder, solvent system, cross-linking agent, catalyst, etc.) can be formed into a mixture and refluxed for about 24 hours under nitrogen. The polymer binders can also be prepared by known methods. For example, the desired monomers can be dissolved in a solvent and polymerized by a free radical polymerization reaction using a catalyst such as 2,2xe2x80x2-azobisisobutyronitrile. Those skilled in the art will appreciate that the reaction conditions, amount of catalyst, and other parameters can be adjusted to control the molecular weight of the final ARC composition.
The resulting ARC composition is subsequently applied to the surface of a substrate (e.g., silicon wafer) by conventional methods, such as by spin-coating, to form an anti-reflective coating layer on the substrate. The substrate and layer combination is baked at temperatures of at least about 160xc2x0 C. The baked layer will generally have a thickness of anywhere from about 500 xc3x85 to about 2000 xc3x85. Next, a photoresist can be applied to the ARC layer followed by exposing the photoresist to light at the desired wavelength, developing the exposed photoresist layer, and etching the developed photoresist layer all according to known procedures.
ARCs according to the invention have a dramatically improved etch rate, particularly those ARCs where halogen atoms are bonded to functional groups of the polymer binder. Thus, the ARCs have an etch selectivity to resist (i.e., the ARC etch rate divided by the photoresist etch rate) of at least about 1.2, preferably at least about 1.4, and more preferably at least about 1.5 when CF4 is used as an etchant. Alternately, the etch rate of ARCs including a polymer binder halogenated on a functional group thereof is at least about 10%, preferably at least about 20%, and more preferably from about 30-100% greater than the etch rate of an ARC which includes the same polymer binder without halogenated functional groups. This faster etch rate is particularly important because prior art ARCs have etched substantially slower than the photoresist layer, thus resulting in overetching of the remaining photoresist layers. Use of faster etching ARCs prevents degradation of the photoresist during etching, which in turn protects the device layers.
Additionally, at 248 nm the inventive ARCs have a k value (i.e., the imaginary component of the complex index of refraction) of at least about 0.3, and preferably at least about 0.4, and have an n value (i.e., the ratio of the speed of light through a vacuum to the speed of light through the particular material) of at least about 1.35, and preferably at least about 1.45. Furthermore, when subjected to a stripping test as defined herein, the inventive ARCs will have a stripping amount of less than about 20 xc3x85, and preferably less than about 10 xc3x85. Finally, the ARCs give an interlayer formation result as defined herein of less than about 40 xc3x85, and preferably less than about 30 xc3x85.